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Which sample is more reliable for a genetic test? | CION Cancer Clinics
For most people, blood and saliva are equally reliable for an inherited cancer gene test, because both carry the DNA you were born with. Blood fails less often. Saliva is easier to give at home. The choice only really matters if you have a blood cancer or have had a donor transplant. This page compares the sample types and explains how to avoid a repeat collection. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- Is blood or saliva more reliable for a gene test?
- How do blood, saliva, cheek swab and skin compare?
- How do you give a saliva sample that works?
- Sample terms you may hear, in plain language
- Which sample suits which situation?
- What this page cannot tell you
- Four things people assume about samples
- Common questions about sample types
The short answer
Is blood or saliva more reliable for a gene test?
For most people, blood and saliva are equally reliable for an inherited cancer gene test. Both carry the same DNA you were born with. Blood gives more DNA and fails less often. Saliva is easier to collect at home and works well for almost everyone when it is given correctly.
What reliable actually means here
A reliable sample does two things. It gives the laboratory enough good DNA to read, and that DNA truly reflects what you inherited. Most failed tests fail on the first point. The sample was too small or spoiled, so it has to be collected again. That costs time, not accuracy.
When the choice genuinely matters
A small group of people should not use blood or saliva at all. If you have a blood cancer, or have had a bone marrow or stem cell transplant from a donor, the DNA in your blood may not be the DNA you inherited. For you, the laboratory usually asks for a small skin sample instead. Tell your counsellor before any sample is taken.
Accuracy depends more on the laboratory's standards than on the sample type.Four sample types
How do blood, saliva, cheek swab and skin compare?
All four can carry your inherited DNA. They differ in how much DNA they give and who they suit.
Blood
The long-standing standard. A normal blood draw from the arm gives a large amount of good DNA, so repeat collection is rare. It needs a visit to a clinic or a collection centre.
Best suited to
- People already having blood tests at the clinic
- Tests that may need extra analysis later
Saliva
You spit into a tube with a preserving liquid. The DNA comes mostly from white cells in the saliva. It can be done at home and couriered, which helps families in districts far from a city centre.
Eating, drinking or chewing paan shortly before can spoil the sample.Cheek swab
A soft brush rubbed inside the cheek. It is quick and suits young children and people who find spitting difficult. It gives the least DNA, so it is more likely to need repeating.
Skin sample
A tiny piece of skin taken under local anaesthetic, then grown in the laboratory. It is used when blood cannot be trusted to show inherited DNA, such as after a donor transplant. It takes longer.
Not sure whether this applies to you?
Ask an oncologistGetting it right first time
How do you give a saliva sample that works?
Nothing in the mouth beforehand
For about half an hour before, do not eat, drink, smoke, chew gum or chew paan or gutka. Food and tobacco dilute the sample and can damage the DNA. Plain water is usually fine earlier on.
Fill to the line, without bubbles
Spit gently until the liquid saliva, not the froth, reaches the line on the tube. Rubbing your cheeks lightly or thinking about food helps. It can take a few minutes, and that is normal.
Close it and mix it properly
Close the cap so the preserving liquid mixes in, then shake as the kit instructs. This liquid is what keeps the DNA stable during the courier journey.
Label it and send it quickly
Check your full name and date of birth on the label. Send it the same day if you can. A wrongly labelled tube cannot be used, however good the sample.
Laboratory words
Sample terms you may hear, in plain language
- Germline sample
- Any sample that carries the DNA you were born with, such as blood, saliva or skin. It is used to look for inherited faults.
- DNA yield
- How much usable DNA the laboratory gets from your sample. Too little and the test cannot run.
- Sample failure
- When the sample cannot be read, usually because there was too little DNA or it was spoiled. You are asked for a new one.
- Mosaicism
- When a gene change is present in some of your cells but not all. It can show up in one sample type more than another.
- Clonal haematopoiesis
- Changes that build up in blood cells with age or after chemotherapy. They can look like an inherited fault on a blood test.
- Cultured skin cells
- Skin cells grown in the laboratory from a small biopsy. They give clean inherited DNA when blood cannot be used.
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Side by side
Which sample suits which situation?
Your situation
Usually preferred
Healthy adult, or a solid tumour such as breast or bowel
Blood or saliva, either is fine
Living far from a collection centre
Saliva kit at home, couriered back
Active leukaemia or another blood cancer
Skin sample, after discussion with the laboratory
Previous donor bone marrow or stem cell transplant
Skin sample, never blood or saliva alone
A relative who has died
Stored tissue block or stored DNA, if available
Being straight with you
What this page cannot tell you
It cannot tell you which sample your own laboratory wants. Each lab validates its test on particular sample types, and some accept only one. Your counsellor will tell you which to give and how. If your result shows a change that might have come from ageing blood, the counsellor may ask for a second sample to confirm it. What your specific variant means is a question for the counsellor who ordered the test.
What sample type does not decide
The laboratory's own quality matters more than whether you gave blood or saliva. Ask whether the laboratory is accredited, for example by NABL in India, and whether it confirms important findings before reporting them.
Who this does not apply to
Tumour testing is a different test on a different sample. It looks for faults inside the cancer to guide treatment, and it is covered under targeted therapy. Most people reading this will not need an inherited gene test at all.
If you have had a blood cancer or a transplant, say so before the sample is taken, not after.Commonly believed
Four things people assume about samples
"Saliva is a cheaper, weaker version of the blood test."
For inherited cancer genes, a good saliva sample gives results that match blood for almost everyone. The main difference is that saliva fails a little more often and may need repeating.
"A tumour sample will tell us about the family too."
Tumour tests look at faults inside the cancer. Some of those are inherited and many are not. A blood or saliva test is still needed to answer the family question properly.
"If my test failed, something must be wrong with my genes."
A failed sample almost always means too little DNA or a spoiled tube. It says nothing about your genes. You simply give another sample.
"A recent blood transfusion ruins the test."
It often does not, but tell the laboratory anyway. They will say whether to go ahead or wait a little before giving the sample.
Questions we are asked
Common questions about sample types
Do I need to fast before a blood sample for a gene test?
No. Fasting does not affect your DNA, so you can eat normally before a blood draw. Fasting only matters for saliva, where food in the mouth can spoil the sample. Follow the instructions that come with your kit or appointment letter.
Can I give the sample during chemotherapy?
Usually yes, for people with solid tumours such as breast, ovarian or bowel cancer. Chemotherapy does not change the DNA you inherited. If your blood counts are very low, the laboratory may prefer saliva or a slightly larger blood sample. Ask your oncologist about timing.
Why would a laboratory ask for a skin sample?
Mainly when your blood may not reflect what you inherited, such as during a blood cancer or after a donor transplant. It is a quick procedure under local anaesthetic. It takes longer because the cells have to be grown before testing.
How long does a saliva sample stay usable?
Once mixed with the preserving liquid, DNA stays stable for a good while at room temperature. Still, send it as soon as you can and keep it out of direct sun. Delays in courier transit are a common reason for repeat requests.
Can a child give a saliva sample?
Young children often cannot spit enough, so a cheek swab or blood sample is used instead. Most inherited cancer testing waits until adulthood anyway. Your counsellor will say whether testing a child is needed at all.
Will a failed sample cost me extra?
Policies differ between laboratories. Many repeat a failed sample at no extra charge, but not all. Ask about this before you pay, especially if you are paying yourself rather than through insurance or a government scheme.
Can my DNA be reused for a later test?
Sometimes. Many laboratories store extracted DNA, which can save you giving a new sample for extra genes later. Storage and reuse need your consent, so check what you agreed to on the consent form.
Who decides which sample I give?
Your counsellor or oncologist, based on your health and what the laboratory accepts. If you are not sure you have been given the right kit, call the CION helpline before sending it.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
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Sources
- MedlinePlus Genetics — How is genetic testing done?
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- NHS — Predictive genetic tests for cancer risk genes
- Cancer Research UK — Inherited cancer genes and increased cancer risk
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Giving the sample: blood, saliva or cheek swabWhat the collection itself involvesCan a genetic test be done from a tissue block?When stored surgery tissue can be usedTesting a deceased relative's stored sampleOptions when the affected relative has diedWhy genetic results take weeksWhat happens to your sample after it leaves you
Talk to us
Not sure which sample you should give?
Tell us about your diagnosis and any treatment so far. We will check which sample suits you before anything is collected. One helpline serves every CION centre.